I have a server running ubuntu 10.04 with four interfaces. eth0 and eth1 have static WAN ip's, and eth2 and eth3 are connected to two separate NAT networks 192.168.0.0/24 and 192.168.1.0/24 respectively. eth0 is masqueraded and NAT traffic from eth2 is forwarded to it. In order to forward eth3 traffic to eth1 I have used these rules:

This setup is working fine. eth1 is masqueraded and NAT traffic from eth3 is forwarded to it. But I feel some rules above are redundant, and there must be a simpler way of achieving it. Are there any better ways of doing it?